[QE-users] Is there any problem if I use less ecutwfc and ecutrho than the suggested value in the pp file?

[ENDALE ABEBE]

Dear Andrii Shyichuk

Thank you for this clear explanation. I remember, I did two EOS
calculations: one with pseudopotential from  http://physics.rutgers.edu/gbrv
the other from QE website; the later did not give me a smooth curve Now
thanks to you I have come  to understand the reason.

By the way, is it possible to use the pseudopotential obtained from
http://physics.rutgers.edu/gbrv for a calculation that includes
spin-orbit-coupling?

With Kind Regards

On Mon, Oct 19, 2020 at 1:19 AM Andrii Shyichuk <
andrii.shyichuk at chem.uni.wroc.pl> wrote:

> Dear Endale,
>
> Using values smaller than recommended might result in errors going
> unpredictably high.
> In your case, using e.g. 40/400 instead of 45/455 could happen to be fine
> (or not), but 30/300 is most likely bad.
>
> In order to check it, try a few calculations with different cutoffs. As
> the cutoff goes up, band gap should approach some value.
> As the cutoff goes down, the point of rapid change in the values is where
> things get bad.
> Same goes for DOS, if it starts to change at lower cutoffs - bad.
>
> Another thing to check is energy-volume curve (equation of state, EOS),
> which should be smooth.
> If it's not - the basis is probably too low.
> And, it's minimum should converge with the increasing cutoffs.
>
> I recommend looking into GBRV pseudopotentials (optimized for about 40 Ry
> cutoff) http://dx.doi.org/10.1016/j.commatsci.2013.08.053.
>
> Finally, check your basis on some known materials that contain the same
> elements as your material of interest.
>
> Best regards.
> Andrii Shyichuk
>
> W dniu 2020-10-20 02:10, ENDALE ABEBE napisał:
>
> Dear Expertise
>
> Let me say I am calculating the energy bandgap of a semiconductor, which
> doesn't have reported value in literature.
> What is the parameter that I need to check to say the ecutwfc/ecutrho is
> sufficient and the value ot energy bandgap is correct?
>
> Thank you for your support
>
> With Best Regards
>
>
> On Tue, Oct 13, 2020 at 1:06 AM Paolo Giannozzi <p.giannozzi at gmail.com>
> wrote:
>
>> As long as your cutoffs are sufficiently good to get the desired accuracy
>> on the targeted properties, there is no problem. The cutoffs suggested in
>> the PP file are on the safe side and thus quite high, if I remember
>> correctly.
>>
>> Paolo
>>
>> On Mon, Oct 12, 2020 at 2:56 PM ENDALE ABEBE <endtse at gmail.com> wrote:
>>
>>> Dear Expertise
>>>
>>> The suggested values of the ecutrho and ecutwfc are making my
>>> calculation expensive. For instance, in the pseudo potential file of Bi,
>>> Bi.pbe-dn-kjpaw_psl.1.0.0.UPF
>>> <https://www.quantum-espresso.org/upf_files/Bi.pbe-dn-kjpaw_psl.1.0.0.UPF>,
>>> these are:
>>>
>>>     Suggested minimum cutoff for wavefunctions:  45. Ry
>>>     Suggested minimum cutoff for charge density: 455. Ry
>>>
>>> Is there any problem if I use less values than these as much as the
>>> total energy of the system converges?
>>>
>>> Thank you in advance for your response.
>>>
>>> With Regards
>>>
>>> --
>>> Endale Abebe
>>> Program coordinator and Lecturer
>>> Faculty of Materials Science and Engineering
>>> Jimma Institute of Technology
>>> Jimma University
>>> P.O.Box 378, Jimma, Ethiopia
>>> Mobile: +251921381598
>>> _______________________________________________
>>> Quantum ESPRESSO is supported by MaX (www.max-centre.eu)
>>> users mailing list users at lists.quantum-espresso.org
>>> https://lists.quantum-espresso.org/mailman/listinfo/users
>>
>>
>>
>> --
>> Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
>> Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
>> Phone +39-0432-558216, fax +39-0432-558222
>>
>> _______________________________________________
>> Quantum ESPRESSO is supported by MaX (www.max-centre.eu)
>> users mailing list users at lists.quantum-espresso.org
>> https://lists.quantum-espresso.org/mailman/listinfo/users
>
>
>
> --
> Endale Abebe
> Program coordinator and Lecturer
> Faculty of Materials Science and Engineering
> Jimma Institute of Technology
> Jimma University
> P.O.Box 378, Jimma, Ethiopia
> Mobile: +251921381598
>
> _______________________________________________
> Quantum ESPRESSO is supported by MaX (www.max-centre.eu)
> users mailing list users at lists.quantum-espresso.orghttps://lists.quantum-espresso.org/mailman/listinfo/users
>
>
>
> _______________________________________________
> Quantum ESPRESSO is supported by MaX (www.max-centre.eu)
> users mailing list users at lists.quantum-espresso.org
> https://lists.quantum-espresso.org/mailman/listinfo/users



-- 
Endale Abebe
Program coordinator and Lecturer
Faculty of Materials Science and Engineering
Jimma Institute of Technology
Jimma University
P.O.Box 378, Jimma, Ethiopia
Mobile: +251921381598
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